Electromagnetic reproducer



March 3, 1931. o. B. PARKER ELECTROMAGNETIC REPRODUCER Filed July 19, 1930 Patented Mar. 3, 1931 UNFTED. stares PATENT eerie OLIVER B. PAR-KER, OF BROOKLYN, YORK, ASSIGNORJTO PACENT ELECTRIC COM- PANY, ING, OF NEW YORK, N. Y.

, A CORPORATION OF NEW" YORK ELECTROMAGNETIC RE]?ROIDUGERv Application filed July 19,

Special objects of the present invention are to provide a reproducer for electric phonographs and the like, which will be of simple, practical construction, small compact deaign, and which will have inherent self-damping characteristics.

The novel features of the invention by which the foregoing and other desirable objects are attained will appear from the following specification.

"The drawing which forms part of the specification is illustrative of a simple commerc'ial embodiment of the invention, it being appreciated that the structure may be moditied and chan ed in various ways without departure' from the true spirit and broad scope of theinvention'.

Fig. 1 is a top plan viewof the device; Fig. 2 is a front viewof the same; Fig. 3

is a bottom plan view;

A strong magnetic field is provided in the form of the invention shown, by a permanent U-magnet 5 of general horseshoe shapes Pole pieces 6, 7, are suitably connected tothe arms of this U-magnet and a coil 8a is supported within the hollows of these pole pieces, which latter, as particularly shown in Fig. 2 are of general C-form and placed in opposing relation, so as to provide pole tips 660, 7a, 67), 7/), forming the two magnetic gaps. at 8 and 0.

Mounted for operation between the pole pieces is an armature or reed 10 extending freely through the open center of the coil and terminating in a blade portion 11, bridging the upper magnetic gap 8. A special feature of this armature blade is that it extends substantially parallel to and overlies the adjacent parallel faces 11, of the upper pole tips 6a, Ta, and that it has a sliding action across said pole faces. To provide for and permit of this sliding movement, the blade portion of the armature is shown as bearing against a sheet of non-magnetic material 12 disposed in bridging relation over the pole faces. This material is preferably relatively thin, so as to bring the active portion of the armature into magnetically close relation to the pole faces. A layer of fish paper insulation has been found suitable for the purpose. this 1930. Serial No. 469,069.

being relatively stiff and exerting a frictional holding force on the armature blade sufficient to exert the desired damping tendency on the same.

To provide'for the desired sliding action across the pole tips, the armature is shown as having a shaft portion 13 held in rubber bushings 14, or the like, between the lower pole tips 66, 71), Fig. 2, this shaft portion being threaded at the front of the unit to receive the screw 15, which secures the stylus 16 in the lower end of the reed.

In order that the various parts of the apparatus may be assembled apart from the magnet and then be applied as a unit to the magnet, the pole pieces are shown as rigidly secured together in proper spaced relation by a bridge plate 17 of non-magnetic material secured to the two pole pieces by the screws 18. This construction enables the armature and the coil to. be properly assembled and the pole pieces rigidly fastened together, with the several parts in properly assembled order and these parts, then forming a single unit, to be secured as sue to the ma gnet. The fastening of the assembled unit to the magnet is shown as accomplished by screws'l9 passed. freely through openings in the magnet arms into screw seats formedin the pole pieces.

' Yhe'n the pole pieces are attached to the. magnet, the end of the armature is attracted to the side faces ofthe pole tips and the armature therefore becomesmagnetically damped. The'sliding movement of the armature across the pole faces is therefore opposed with amagnetic braking effect and by the frictionalresistanceinterposed between the blade of-the reed and the adjacent polar faces. The de-.-

gree of damping may be determined by the nature-and thickness of material between the pole faces and armature blade. Preferably, this material is relatively thin, so as to; keep themagnetic reluctance low and hence make the device sensitive andefticient. This construction, in which the" armature slides-over thepole faces, across the gap,'eliniinates the need for any fine adjustments, such as are necessary in constructions'where the armature operates within the gap and provides a simpler and more inexpensive construction.

The movement of the armature is relatively slight and the area of actual physical contact may be small, so that a proper degree of damping is obtained without impairing the efiiciency of the device. lVhile the blade of the armature is shown as substantially overlapping both polar faces at opposite sides of the gap, the degree of overlap may be less or more, special conditions may require. The blade is usually substantially flat, so as to be parallel with the polar faces at the points or areas of contact.

By reason of the sliding action across the pole faces, the resistance to movement is substantially uniform throughout the usual range of action of the armature.

The invention also provides a particularly compact and small unit. The upper polar extensions 6a, 7a, are indicated in Figs. 1 and 2 as cut back at 20 to approximately half the normal width to concentrate the magnetic flux through the armature and to enable the location of the armature on the intermediate portion of its shaft, where it is supported by hearing portions at both sides of the same.

hat is claimed is:

1. In a device of the character disclosed, the combination of pole pieces spaced to form a magnetic gap and a movable armature having a sliding engagement across the faces of said pole pieces at opposite sides of said gap.

2. In a device of the character disclosed, the combination of pole pieces spaced to form a magnetic gap, a movable armature having a sliding engagement across the faces of said pole pieces at opposite sides of said gap, there being a thin layer of non-magnetic material interposed between said armature and pole faces preventing direct physical contact between the armature and pole faces.

3. An electromagnetic unit, comprising a magnet having pole pieces separated to pro vide a magnetic gap and a movable armature bridging said gap and having physical. engagement with the polar structure providing said gap.

4. An electromagnetic unit, comprising a magnet having pole pieces separated to provide a magnetic gap, a movable armature bridging said gap and having physical engagement with the polar structure providing said gap and a coil inductively related to said armature.

5. An electromagnetic unit, comprising a magnet having pole pieces separated to provide a magnetic gap, a movable armature bridging said gap and having physical engagement with the polar structure providing said gap and a thin layer of non-magnetic material interposed between the armature and adjacent polar faces.

6. In a device of the character disclosed. substantially C-shaped pole pieces arranged in opposition to provide two magnetic gaps,

an armature having a shaft portion mounted in one of said gaps and having a blade portion sliding across the polar faces of the other gap.

7. In a device of the character disclosed, substantially C-shaped pole pieces arranged in opposition to provide two magnetic gaps, an armature having a shaft portion mounted in one of said gaps and having a blade portion sliding across the polar faces of the other gap and a coil surrounding said armature and disposed within the hollows of the C-shaped pole pieces.

8. In an instrument of the character disclosed, magnetic pole pieces spaced to form a magnetic gap, an armature mounted for movement across said gap, non-magnetic material extending across the gap, said armature resting on said nonmagnetic material, a coil inductively related to said armature and mechanical power transmission means connected with said armature.

9. An electromagnetic device, comprising a magnet having pole pieces separated to provide a magnetic gap, a thin layer of nonmagnetic material bridging said gap, a vibratory armature slidingly engaging said bridging layer of non-magnetic material, a winding associated with said armature and mechanical power transmission means connected with said armature.

10. An electrical instrument comprising a magnet having pole pieces separated by a magnetic gap, a sheet of insulation bridging said magnetic gap, an armature mounted for movement across said gap and bearing on said sheet of insulation and power transmission means connected with said armature.

In testimony whereof, I aliix my signature.

OLIVER B. PARKER. 

